High-strength corrosion-resistant reinforcing steel and method of making same

Abstract

The present application belongs to the technical field of steel preparation, and particularly relates to a high-strength corrosion-resistant steel bar and a preparation method thereof. Raw materials of the high-strength corrosion-resistant steel bar comprise the following components: C 0.025-0.035%, Cu 0.75-0.85%, Cr 0.45-0.55%, Ni 0.35-0.45%, Mo 0.18-0.22%, Nb 0.022-0.028%, V 0.035-0.05%, Ti 0.01-0.025%, B 0.0008-0.0012%, Si 0.25-0.35%, Mn 0.7-0.9%, La 0.006-0.008%, Ce 0.006-0.008%, and the rest is Fe and inevitable impurities. The present application adopts ultra-low carbon smelting, rare earth purification, controlled rolling and controlled cooling, and plating process, realizes steel bar organization refinement and double corrosion prevention, and has high strength and corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of steel preparation technology, specifically relating to a high-strength corrosion-resistant steel bar and its preparation method. Background Technology

[0002] In modern infrastructure construction, steel reinforcement, as a key skeletal material for concrete structures, directly determines the safety, durability, and economy of the project. While traditional carbon steel reinforcement has a cost advantage, it is prone to corrosion and expansion in humid, salt spray, or acidic environments, leading to cracking and spalling of the concrete cover and ultimately structural failure. With the rapid development of large-scale cross-sea bridges, deep-sea ports, buildings in saline-alkali areas, and super high-rise structures, unprecedentedly stringent requirements have been placed on steel reinforcement materials. On the one hand, structural design increasingly pursues lightweighting and large spans, urgently requiring steel reinforcement with higher strength grades to reduce cross-sectional dimensions and material usage, thus optimizing structural design. On the other hand, these structures are often exposed to environments rich in chloride ions (such as marine environments and de-icing salt) or high humidity and highly corrosive media for extended periods, making steel reinforcement corrosion a major threat to the structural service life. While the strength of traditional ordinary strength steel reinforcement or conventional high-strength steel reinforcement has increased, its corrosion resistance has often not improved simultaneously, and may even be exacerbated by changes in microstructure. Simply relying on passive protective measures such as increasing the thickness of the concrete cover or improving the density of the concrete not only increases construction costs and structural weight, but also has limited effectiveness and is insufficient to meet the needs of projects with ultra-long design lifespans. Therefore, based on the above issues, it is extremely necessary to develop a new type of steel reinforcement that combines high strength with excellent corrosion resistance. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the purpose of this invention is to provide a high-strength corrosion-resistant steel bar and its preparation method.

[0004] The technical effect described in this invention is achieved through the following technical solution: a high-strength corrosion-resistant steel bar, the raw materials of which include the following components in percentage: C 0.025-0.035%, Cu 0.75-0.85%, Cr 0.45-0.55%, Ni 0.35-0.45%, Mo 0.18-0.22%, Nb 0.022-0.028%, V 0.035-0.05%, Ti 0.01-0.025%, B 0.0008-0.0012%, Si 0.25-0.35%, Mn 0.7-0.9%, La 0.006-0.008%, Ce 0.006-0.008%, with the remainder being Fe and unavoidable impurities.

[0005] Preferably, another aspect of the present invention provides a method for preparing high-strength corrosion-resistant steel bars, comprising the following preparation steps:

[0006] S1: Raw material smelting and composition adjustment: Molten iron and clean scrap steel are charged into the converter according to the heat balance ratio. 90 seconds before the end of blowing, Cu, Cr, Ni and Mo alloy ladles are added sequentially. At the end of blowing, deoxidizer FeSi is added. The carbon content at the end is controlled at 0.025-0.035 wt%. After tapping, Ar-N mixed gas is introduced into the ladle and stirred for 6 minutes to uniformly dissolve Nb, V and Ti microalloyed wires. When the total oxygen in the ladle is ≤30ppm, it is transferred to the next refining stage.

[0007] S2: RH Vacuum and LF Ultra-Clean Refining: After completing step S1, place the ladle in the RH vacuum chamber, evacuate to 2 mbar, and set the argon riser flow rate to 7 N m³. 3 / t, process for 5-8 minutes; after returning to atmospheric pressure, transfer to LF refining furnace; feed Ca wire at a Ca / Al ratio of 1:0.55-0.6 within the first 8 minutes, and maintain the molten steel temperature at 1610-1620℃. After Ca treatment, continue to feed FeB cored wire at a feed rate of 0.8-1.2 kg / t. The oxygen potential at the refining endpoint is ≤18ppm, and then proceed to the next continuous casting step.

[0008] S3: Rare earth wire feeding and light pressing in continuous casting zone: After completing step S2, the Ø11mm La-Ce cored wire feeder is started simultaneously during ladle casting. La-Ce mixed rare earth is added slowly and uniformly at a depth of 70mm in the molten steel in the crystallizer. The slag surface is covered with low-viscosity emulsified powder. A 150mm×150mm square billet is used to apply 0.8mm light pressing in the secondary cooling zone and is cooled to 730℃ at a mist cooling rate of 3°C / s.

[0009] S4: Thermomechanical Controlled Rolling: After completing step S3, the billet is hot-sent into a walking beam heating furnace, with a homogenization temperature of 1050-1080℃ for 20-30 minutes. In the roughing zone, the temperature drops from 1050-1080℃ to 980℃, with a total reduction of 30%. In the finishing zone, the temperature drops from 980℃ to 880℃, with a reduction of 45%. The finished steel bars are uniformly conveyed through a 2m discharge roller conveyor, and the average temperature of the steel bars is maintained at 870-880℃.

[0010] S5: Online quenching: After completing step S4, the rolled 16-25mm steel bars are uniformly introduced into the water mist-air curtain combined quenching box. When the temperature cools to 260℃, it is held for 1-1.5s, and then naturally convectively cooled to 100℃.

[0011] S6: Medium-temperature distribution and tempering: After completing step S5, the steel bars are removed from the quenching box and heated to 430-460℃ via a 14m slide rail, held at a constant temperature for 100-140s, and then air-cooled to room temperature.

[0012] S7: Zn-Al-Mg micro-plating and rare earth post-treatment: After completing step S6, heat the steel bar to 510-530℃, and then immerse it in a Zn-Al-Mg liquid bath at 470-490℃ for 2-3 seconds; after removing it from the bath, use an air knife to quantitatively control the coating, and place the steel bar in room temperature humid air for 7-10 days to carry out deliquescence-drying cycle;

[0013] S8: Finished product aging and inspection: After the finished steel bars are treated at 160℃ for 2 hours and then naturally aged at 20-35℃ for 48 hours, the entire steel bar is subjected to non-destructive testing using electromagnetic eddy current and online ultrasonic equipment, and then cut and bundled according to length.

[0014] Preferably, in step S1, the molten iron has P ≤ 0.03% and S ≤ 0.015%;

[0015] Preferably, in step S1, the weight ratio of molten iron to scrap steel is 68-72:28-32;

[0016] Preferably, in step S1, the Ar-N mixed gas flow rate is: Ar 30 L / min, N 20 L / min;

[0017] Preferably, in step S3, the specific parameters for the uniform and slow addition are: 1 to 1.5 m / min;

[0018] Preferably, in step S3, the low-viscosity emulsifying powder is composed of CaO, SiO2, Al2O3, CaF2, Na2O, K2O and C in a mass ratio of 29-33:30-32:5:6:3:5:4.

[0019] Preferably, in step S5, the steel bar introduction speed parameter is 8-10 m / min;

[0020] Preferably, in step S5, the parameters of the water mist-air curtain combined quenching box are: water pressure of the water mist section 0.45~0.65MPa, compressed air pressure of the air curtain section 0.25~0.35MPa, length of the water mist section 1.2~1.5m, and length of the air curtain section 0.6~0.8m;

[0021] Preferably, in step S7, the Zn-Al-Mg liquid tank is composed of the following raw materials in percentage: Zn 96.6-97.6%, Al 1.2-1.7%, Mg 1.2-1.7%;

[0022] Preferably, in step S7, the quantitative control parameter for the coating is 25–35 g / m³. 2 ;

[0023] Preferably, in step S7, the parameters of the ambient temperature and humidity air are: temperature 20-30℃, relative humidity 70-80%.

[0024] The beneficial effects of this invention are as follows:

[0025] The process of this invention unfolds in the order of steelmaking purification, microstructure refinement, phase transformation stabilization, and surface synergistic protection, with parameters in each stage interconnected and working together. In the smelting stage, ultra-low carbon molten iron is used as the base, utilizing the high-temperature solidification of Cu, Cr, Ni, and Mo pre-alloyed at the end of the converter process to avoid early precipitation; subsequently, vacuum degassing controls residual hydrogen and total oxygen at low levels. Ca treatment converts sharp-angled Al2O3 into calcium aluminate, followed by feeding La-Ce cored wire under low oxygen potential conditions. Rare earth reacts with calcium to generate fine complex oxygen and sulfide inclusions, reducing the probability of crack initiation and mitigating central component segregation during continuous casting. Light reduction and mist cooling are implemented in the secondary cooling zone of continuous casting, causing columnar crystals to break and diluting elemental banding segregation, providing a uniform matrix for subsequent hot working; thermomechanically controlled rolling selects the non-recrystallization temperature zone during staged cooling, combined with finishing rolling reduction, to simultaneously form high-density dislocations and Nb-Ti-V carbonitride nanoprecipitates. After rolling, the steel bars are not subjected to a long cooling bed and are directly placed into a water mist-air curtain combined quenching box, where they are rapidly cooled from a high temperature to a lower temperature with a short pause, generating fine acicular martensite while retaining some supercooled austenite. The distribution-tempering stage promotes the redistribution of carbon between the retained austenite and martensite, stabilizing the retained austenite; at the same time, ε-Cu atomic groups and secondary NbC / V(C,N) precipitation are formed. These two types of particles lock dislocations and compensate for insufficient solid solution strengthening caused by ultra-low carbon, thereby improving yield strength while maintaining good ductility and inhibiting temper embrittlement. The surface treatment uses Zn-Al-Mg alloy liquid immersion plating. The fine MgZn2 grains in the coating first act as sacrificial anodes, and after dissolution, they generate dense corrosion products containing Mg and Zn on the surface, reducing the subsequent dissolution rate; rare earth elements are enriched at the steel-coating interface during the high-temperature oxidation stage, which is conducive to the transformation of γ-FeOOH to the more dense α-FeOOH structure and shortens the densification time of the rust layer. Therefore, the outer sacrificial anode protection and the inner repassivation film together form a dual barrier, which can delay pitting corrosion propagation and reduce the long-term corrosion rate. After the finished steel bars are treated with low-temperature heating stress relaxation followed by natural aging at room temperature for 48 hours, the residual austenite is further stabilized and the local processing stress peak is relaxed. Electromagnetic eddy current and ultrasonic testing perform non-destructive testing on the entire steel bar with equivalent sensitivity of Φ1mm flat-bottom reflection, which can eliminate surface defects and identify internal microcracks or interconnected inclusions, ensuring that the product is in a state of low defects, low residual stress, and surface passivation mechanism activated, thereby achieving the comprehensive performance goals of high strength, corrosion resistance, and weldability. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 These are the results of the red rust area test of the steel bars in Embodiment 1 and Comparative Examples 1-3 of this invention.

[0028] Figure 2 This is a graph showing the mass loss results of salt spray corrosion protection tests on the reinforcing bars of Embodiment 1 and Comparative Examples 1-3 of the present invention;

[0029] Figure 3 This is a SEM (Scanning Electron Microscope) image of the salt spray corrosion resistance test after Example 1 of the present invention;

[0030] Figure 4 This is a SEM (Scanning Electron Microscope) image of the salt spray corrosion resistance test of Comparative Example 1 of this invention. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that, unless otherwise specified, the raw materials involved in the present invention are all purchased through conventional commercial channels.

[0032] Example 1: A high-strength corrosion-resistant steel bar, the raw materials of which include the following components in percentage: C 0.035%, Cu 0.85%, Cr 0.55%, Ni 0.45%, Mo 0.22%, Nb 0.028%, V 0.05%, Ti 0.025%, B 0.0012%, Si 0.35%, Mn 0.9%, La 0.008%, Ce 0.008%, with the remainder being Fe and unavoidable impurities.

[0033] The preparation steps of the high-strength corrosion-resistant steel bars are as follows:

[0034] S1: Raw material smelting and composition adjustment: Molten iron with P≤0.03% and S≤0.015% and clean scrap steel are mixed in a heat balance ratio of 68:32 and charged into the converter. 90 seconds before the end of blowing, Cu, Cr, Ni, and Mo alloy ladles are added sequentially. At the end of blowing, deoxidizer FeSi is added, and the carbon content at the end is controlled at 0.035wt%. After tapping, Ar-N mixed gas is introduced into the ladle at a rate of Ar 30L / min and N 20L / min and stirred for 6 minutes to uniformly dissolve Nb, V, and Ti microalloyed wires. When the total oxygen in the ladle is ≤30ppm, it is transferred to the next refining stage.

[0035] S2: RH Vacuum and LF Ultra-Clean Refining: After completing step S1, place the ladle in the RH vacuum chamber, evacuate to 2 mbar, and set the argon riser flow rate to 7 N m³. 3 / t, process for 5min; after returning to atmospheric pressure, transfer to LF refining furnace; feed Ca wire at a Ca / Al ratio of 1:0.55 within the first 8min, keep the molten steel temperature at 1620℃, after Ca treatment, continue to feed FeB cored wire at a feed rate of 1.2kg / t, the oxygen potential at the refining endpoint is ≤18ppm, and then proceed to the next continuous casting step;

[0036] S3: Rare earth wire feeding and light pressing in continuous casting zone: After completing step S2, the Ø11mm La-Ce cored wire feeder is started simultaneously during ladle casting. La-Ce mixed rare earth is added slowly at a uniform speed of 1.5m / min at a depth of 70mm in the molten steel in the crystallizer. The slag surface is covered with a low-viscosity emulsion powder composed of CaO, SiO2, Al2O3, CaF2, Na2O, K2O and C in a mass ratio of 33: 32:5:6:3:5:4. A 150mm×150mm square billet is used to implement light pressing of 0.8mm in the secondary cooling zone and is cooled to 730℃ at a mist cooling rate of 3°C / s.

[0037] S4: Thermomechanical Controlled Rolling: After completing step S3, the billet is hot-sent into a walking beam heating furnace, with a homogenization temperature of 1080℃ and a time of 20 minutes. The temperature in the roughing zone drops from 1080℃ to 980℃, with a total reduction of 30%. The temperature in the finishing zone drops from 980℃ to 880℃, with a reduction of 45%. The steel bars exiting the finishing zone are uniformly conveyed via a 2m discharge roller conveyor, and the average temperature of the steel bars is maintained at 880℃.

[0038] S5: Online quenching: After completing step S4, the rolled 16mm steel bar is introduced into the water mist-air curtain combined quenching box at a uniform speed of 10m / min. The water pressure in the water mist section is 0.65MPa, the compressed air pressure in the air curtain section is 0.35MPa, the length of the water mist section is 1.5m, and the length of the air curtain section is 0.8m. When the temperature cools to 260℃, it is held for 1s, and then naturally convectively cooled to 100℃.

[0039] S6: Medium-temperature distribution and tempering: After completing step S5, the steel bar is removed from the quenching box and heated to 460℃ via a 14m slide rail, held at the constant temperature for 100s, and then air-cooled to room temperature.

[0040] S7: Zn-Al-Mg micro-plating and rare earth post-treatment: After completing step S6, the steel bar is heated to 530℃, and then immersed in a Zn-Al-Mg bath at 490℃ (composed of 97% Zn, 1.5% Al, and 1.5% Mg) for 2 seconds; after removal from the bath, an air knife is used to quantitatively control the coating to 35g / m². 2 The steel bars were placed at 20°C and 70% relative humidity for 7 days to undergo a deliquescence-drying cycle.

[0041] S8: Finished product aging and inspection: After the finished steel bars are treated at 160℃ for 2 hours and then naturally aged at 20℃ for 48 hours, the entire steel bar is subjected to non-destructive testing using electromagnetic eddy current and online ultrasonic equipment. The ultrasonic longitudinal wave flaw detection sensitivity reaches the equivalent defect of Φ1mm flat bottom hole reflection. Subsequently, the steel bars are cut and bundled according to length.

[0042] Example 2: A high-strength corrosion-resistant steel bar, the raw materials of which include the following components in percentage: C 0.03%, Cu 0.8%, Cr 0.5%, Ni 0.4%, Mo 0.2%, Nb 0.025%, V 0.043%, Ti 0.018%, B 0.001%, Si 0.3%, Mn 0.8%, La 0.007%, Ce 0.007%, with the remainder being Fe and unavoidable impurities.

[0043] The preparation steps of the high-strength corrosion-resistant steel bars are as follows:

[0044] S1: Raw material smelting and composition adjustment: Molten iron with P≤0.03% and S≤0.015% and clean scrap steel are mixed in a heat balance ratio of 70:30 and charged into the converter. 90 seconds before the end of blowing, Cu, Cr, Ni, and Mo alloy ladles are added sequentially. At the end of blowing, deoxidizer FeSi is added, and the carbon content at the end is controlled at 0.03wt%. After tapping, Ar-N mixed gas is introduced into the ladle at a rate of Ar 30L / min and N 20L / min and stirred for 6 minutes to uniformly dissolve Nb, V, and Ti microalloyed wires. When the total oxygen in the ladle is ≤30ppm, it is transferred to the next refining stage.

[0045] S2: RH Vacuum and LF Ultra-Clean Refining: After completing step S1, place the ladle in the RH vacuum chamber, evacuate to 2 mbar, and set the argon riser flow rate to 7 N m³. 3 / t, process for 7min; after returning to atmospheric pressure, transfer to LF refining furnace; feed Ca wire at a Ca / Al ratio of 1:0.57 within the first 8min, keep the molten steel temperature at 1615℃, after Ca treatment, continue to feed FeB cored wire at a feed rate of 1kg / t, the oxygen potential at the refining endpoint is ≤18ppm, and then proceed to the next continuous casting step.

[0046] S3: Rare earth wire feeding and light pressing in continuous casting zone: After completing step S2, the Ø11mm La-Ce cored wire feeder is started simultaneously during ladle casting. La-Ce mixed rare earth is added slowly at a uniform speed of 1.2m / min at a depth of 70mm in the molten steel in the crystallizer. The slag surface is covered with a low-viscosity emulsion powder composed of CaO, SiO2, Al2O3, CaF2, Na2O, K2O and C in a mass ratio of 31:31:5:6:3:5:4. A 150mm×150mm square billet is used to implement light pressing of 0.8mm in the secondary cooling zone and is cooled to 730℃ at a mist cooling rate of 3°C / s.

[0047] S4: Thermomechanical Controlled Rolling: After completing step S3, the billet is hot-sent into a walking beam heating furnace, with a homogenization temperature of 1065℃ and a time of 25 minutes. The temperature in the roughing zone drops from 1065℃ to 980℃, with a total reduction of 30%. The temperature in the finishing zone drops from 980℃ to 880℃, with a reduction of 45%. The steel bars exiting the finishing zone are uniformly conveyed via a 2m discharge roller conveyor, and the average temperature of the steel bars is maintained at 875℃.

[0048] S5: Online quenching: After completing step S4, the rolled 20mm steel bar is introduced into the water mist-air curtain combined quenching box at a uniform speed of 9m / min. The water pressure in the water mist section is 0.55MPa, the compressed air pressure in the air curtain section is 0.3MPa, the length of the water mist section is 1.3m, and the length of the air curtain section is 0.7m. When the temperature cools to 260℃, it is held for 1.2s, and then naturally convectively cooled to 100℃.

[0049] S6: Medium-temperature distribution and tempering: After completing step S5, the steel bar is removed from the quenching box and heated to 445℃ via a 14m slide rail, held at the constant temperature for 120s, and then air-cooled to room temperature.

[0050] S7: Zn-Al-Mg micro-plating and rare earth post-treatment: After completing step S6, the steel bar is heated to 520℃, and then immersed in a Zn-Al-Mg bath at 480℃ (composed of 96.6% Zn, 1.7% Al, and 1.7% Mg) for 2.5 seconds; after removal from the bath, an air knife is used to quantitatively control the coating to 30g / m². 2 The steel bars were placed at 25°C and 75% relative humidity for 8 days to undergo a deliquescence-drying cycle.

[0051] S8: Finished product aging and inspection: After the finished steel bars are treated at 160℃ for 2 hours and then naturally aged at 27℃ for 48 hours, the entire steel bar is subjected to non-destructive testing using electromagnetic eddy current and online ultrasonic equipment. The ultrasonic longitudinal wave flaw detection sensitivity reaches the equivalent defect of Φ1mm flat bottom hole reflection. Subsequently, the steel bars are cut and bundled according to length.

[0052] Example 3: A high-strength corrosion-resistant steel bar, the raw materials of which include the following components in percentage: C 0.025%, Cu 0.75%, Cr 0.45%, Ni 0.35%, Mo 0.18%, Nb 0.022%, V 0.035%, Ti 0.01%, B 0.0008%, Si 0.25%, Mn 0.7%, La 0.006%, Ce 0.006%, with the remainder being Fe and unavoidable impurities.

[0053] The preparation steps of the high-strength corrosion-resistant steel bars are as follows:

[0054] S1: Raw material smelting and composition adjustment: Molten iron with P≤0.03% and S≤0.015% and clean scrap steel are mixed in a heat balance ratio of 72:28 and charged into the converter. 90 seconds before the end of blowing, Cu, Cr, Ni, and Mo alloy ladles are added sequentially. At the end of blowing, deoxidizer FeSi is added, and the carbon content at the end is controlled at 0.025wt%. After tapping, Ar-N mixed gas is introduced into the ladle at a rate of Ar 30L / min and N 20L / min and stirred for 6 minutes to uniformly dissolve Nb, V, and Ti microalloyed wires. When the total oxygen in the ladle is ≤30ppm, it is transferred to the next refining stage.

[0055] S2: RH Vacuum and LF Ultra-Clean Refining: After completing step S1, place the ladle in the RH vacuum chamber, evacuate to 2 mbar, and set the argon riser flow rate to 7 N m³. 3 / t, process for 8min; after returning to atmospheric pressure, transfer to LF refining furnace; feed Ca wire at a Ca / Al ratio of 1:0.6 within the first 8min, keep the molten steel temperature at 1610℃, after Ca treatment, continue to feed FeB cored wire at a feed rate of 0.8kg / t, the oxygen potential at the refining endpoint is ≤18ppm, and then proceed to the next continuous casting step.

[0056] S3: Rare earth wire feeding and light pressing in continuous casting zone: After completing step S2, the Ø11mm La-Ce cored wire feeder is started simultaneously during ladle casting. La-Ce mixed rare earth is added slowly at a uniform speed of 1m / min at a depth of 70mm in the molten steel in the crystallizer. The slag surface is covered with a low-viscosity emulsified powder composed of CaO, SiO2, Al2O3, CaF2, Na2O, K2O and C in a mass ratio of 33:32:5:6:3:5:4. A 150mm×150mm square billet is used to implement light pressing of 0.8mm in the secondary cooling zone and is cooled to 730℃ at a mist cooling rate of 3°C / s.

[0057] S4: Thermomechanical Controlled Rolling: After completing step S3, the billet is hot-sent into a walking beam heating furnace, with a homogenization temperature of 1050℃ and a time of 30 minutes. The temperature in the roughing zone drops from 1050℃ to 980℃, with a total reduction of 30%. The temperature in the finishing zone drops from 980℃ to 880℃, with a reduction of 45%. The steel bars exiting the finishing zone are uniformly conveyed via a 2m discharge roller conveyor, and the average temperature of the steel bars is maintained at 870℃.

[0058] S5: Online quenching: After completing step S4, the rolled 25mm steel bar is introduced into the water mist-air curtain combined quenching box at a uniform speed of 8m / min. The water pressure in the water mist section is 0.45MPa, the compressed air pressure in the air curtain section is 0.25MPa, the length of the water mist section is 1.2m, and the length of the air curtain section is 0.6m. When the temperature cools to 260℃, it is held for 1.5s, and then naturally convectively cooled to 100℃.

[0059] S6: Medium temperature distribution and tempering: After completing step S5, the steel bar is removed from the quenching box and heated to 430℃ via a 14m slide rail, held at the constant temperature for 140s, and then air-cooled to room temperature.

[0060] S7: Zn-Al-Mg micro-plating and rare earth post-treatment: After completing step S6, the steel bar is heated to 510℃, and then immersed in a Zn-Al-Mg bath at 470℃ (composed of 97.6% Zn, 1.2% Al, and 1.2% Mg) for 3 seconds; after removal from the bath, an air knife is used to quantitatively control the coating to 25g / m². 2 The steel bars were placed at 30℃ and 80% relative humidity for 10 days to undergo a deliquescence-drying cycle.

[0061] S8: Finished product aging and inspection: After the finished steel bars are treated at 160℃ for 2 hours and then naturally aged at 35℃ for 48 hours, the entire steel bar is subjected to non-destructive testing using electromagnetic eddy current and online ultrasonic equipment. The ultrasonic longitudinal wave flaw detection sensitivity reaches the equivalent defect of Φ1mm flat bottom hole reflection. Subsequently, the steel bars are cut and bundled according to length.

[0062] Comparative Example 1: The operating parameters of Comparative Example 1 and Example 1 are basically the same. The difference is that in Comparative Example 1, La-Ce cored wire is not fed and the surface is only hot-dip galvanized, without Al or Mg. The remaining chemical composition and process are completely maintained.

[0063] Comparative Example 2: The operating parameters of Comparative Example 2 and Example 1 are basically the same. The difference is that the Cu and B contents in Comparative Example 2 are adjusted to Cu 0.05% and B 0.0003% respectively, while the other chemical components and processes are completely maintained.

[0064] Comparative Example 3: The operation parameters of Comparative Example 3 and Example 1 are basically the same. The difference is that in Comparative Example 3, after finishing rolling, it is directly water-cooled to 650°C, then isothermally cooled to 450°C and naturally air-cooled; finally, it is tempered at 550°C for 30 minutes in a conventional manner, without online quenching and medium-temperature distribution and tempering operations. The remaining chemical composition and process are completely maintained.

[0065] Performance testing:

[0066] Mechanical property testing: The yield strength (Ryield) of the steel reinforcement samples prepared in Examples 1-3 and Comparative Examples 1-3 was tested according to GB / T 228.1-2021 standard. eL ), tensile strength (R) m The following tests were conducted: 1) Elongation at break (A); 2) Impact toughness was determined according to GB / T 229-2020 standard, V-notch impact energy, and test temperature -40℃; 3) Residual stress was determined according to GB / T 31310-2014 standard; 4) Three parallel tests were performed for each test, and the average value of the results was taken and retained to one decimal place. The results are shown in Table 1.

[0067] Table 1. Test results of mechanical properties of reinforcing steel bars

[0068]

[0069] As shown in Table 1, the embodiments of the present invention achieve a synergistic effect of high strength and toughness through La-Ce microalloying to capture hydrogen, B element to suppress brittle grain boundary phases, and ε-Cu cluster strengthening, resulting in steel bars with good mechanical properties. In particular, the three key indicators of high yield strength, high tensile strength, and low residual stress are synergistically optimized, and heat treatment and natural aging effectively reduce the residual stress of the steel bars. As shown in Comparative Example 1, without La-Ce cored wire, the mechanical properties are slightly reduced, with only impact toughness and yield strength showing a certain degree of decrease. This may be because the absence of La-Ce cored wire leads to the lack of rare earth grain boundary purification, resulting in a decrease in dislocation slip resistance. Figure 1 , Figure 2 , Figure 3 and Figure 4The results showed that the oxide layer lost its RE enrichment at the interface, resulting in a lower passivation rate. The protective mechanism was similar to that of a pure zinc coating, primarily based on Zn sacrificial anodic dissolution. The pure zinc coating lacked the self-sealing effect of MgZn2 / LDH deposition, and the surface was dominated by a loose γ-FeOOH rust layer. Although Comparative Example 1 showed a slight decrease in mechanical properties compared to Example 1, it exhibited a significant disadvantage in corrosion resistance, with a marked decrease in corrosion resistance. The results of Comparative Example 2 indicated that reducing the Cu and B content may have led to insufficient precipitation of ε-Cu nanoclusters, resulting in reduced yield strength and tensile strength. The content of B decreased significantly; in addition, the reduction in B content may weaken the austenite grain boundary segregation, reduce hardenability, and lead to a decrease in impact toughness. As shown in the results of Comparative Example 3, after fine rolling, rapid cooling and isothermal tempering resulted in the absence of fine needle-like martensite. The precipitation of NbC and ε-Cu was dominated by long tempering at 550℃, resulting in coarse grain size and loss of dislocation pinning ability. Air cooling to 450℃ combined with natural air cooling resulted in a large amount of bainite and a significantly reduced proportion of residual austenite. This made it unable to buffer hydrogen diffusion and local stress. Moreover, the difference in cooling rate between the core and the surface during air cooling caused high tensile stress, which became the source of stress corrosion cracking. Therefore, its mechanical properties decreased significantly compared to Example 1.

[0070] Salt spray corrosion test: According to GB / T 10125-2021 standard, steel bar samples (16×100mm) prepared in Example 1 and Comparative Examples 1-3 were used. The test conditions were 5% NaCl solution, pH=6.5, temperature 35℃, and relative humidity 95%. The test cycles were 500h, 1000h, and 3000h. The evaluation indicators were the red rust area ratio (%) and the mass loss rate (%). Each test was performed in triplicate, and the average value was taken. The results are as follows: Figure 1 and Figure 2 As shown.

[0071] Depend on Figure 1 and Figure 2The results show that the steel bars prepared in this embodiment of the invention achieve long-term corrosion resistance through a triple protection mechanism: the Zn-Al-Mg coating forms a self-healing layered double hydroxide (LDH) barrier during corrosion, effectively blocking chloride ion penetration; rare earth elements (La / Ce) refine the morphology of inclusions and eliminate the local micro-cell effect; and Cu / Ni / Cr alloying elements promote the formation of a dense passivation film, forming a stable rust layer structure. As shown in Comparative Example 1, the initial corrosion products of the pure zinc coating are loose and porous, lacking the dynamic repair function of LDH involving Al / Mg. The lack of rare earth elements causes the inclusions in the steel matrix to maintain sharp edges and corners, becoming stress concentration points and corrosion initiation sources, resulting in a significant increase in the corrosion rate. As shown in Comparative Example 2, insufficient Cu leads to a lack of copper oxide network in the rust layer, making it impossible to form a continuous protective rust layer. Severe B deficiency triggers chain precipitation of carbides at grain boundaries, forming preferential corrosion channels. As shown in Comparative Example 3, the coarse carbonitrides formed during rapid cooling form galvanic cell pairs with the matrix, while the residual stress field induces a microcrack network, providing a rapid channel for the diffusion of corrosive media.

[0072] Cyclic corrosion test: Following GB / T 20854-2007 standard, steel reinforcement samples prepared in Example 1 and Comparative Example 1 were used. The test conditions were: salt spray (4h, 35℃), drying (2h, 60℃), and wetting (18h, 50℃, 95% humidity) as one cycle, for a total of 60 cycles. After the test, SEM (Scanning Electron Microscopy) images were obtained, and the results are as follows: Figure 3 and Figure 4 As shown.

[0073] Figure 3 The image shows that the SEM image of Example 1 shows dense, interconnected flower-shaped / mound-like particles with a single diameter of about 1 to 2 µm; there are almost no through cracks between the particles, the pores are mainly fine pits, and the overall gray scale is uniform, which is consistent with the α-FeOOH and (Mg,Al)-LDH composite film formed after salt spray cycling of the Zn-Al-Mg-rare earth system; it is consistent with the expected dense, self-passivating rust layer; Figure 4 The images show that, in Comparative Example 1, the surface of the SEM image is still dominated by rounded particles, but the distribution is sparse and the boundaries are blurred; pits and cracks are significantly increased, and large openings are visible in some areas. This may be due to insufficient dense α phase, resulting in discontinuous protective film. In addition, the background gray level in the image is uneven, and the micro-area reflectance is greatly different, which is consistent with the morphology of loosely accumulated and locally exposed γ-FeOOH of Zn chloride corrosion products generated by pure zinc coating under the same cycling conditions.

[0074] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-strength, corrosion-resistant steel bar, characterized in that, Its constituent raw materials include the following components in percentage: C 0.025-0.035%, Cu 0.75-0.85%, Cr 0.45-0.55%, Ni 0.35-0.45%, Mo 0.18-0.22%, Nb 0.022-0.028%, V 0.035-0.05%, Ti 0.01-0.025%, B 0.0008-0.0012%, Si 0.25-0.35%, Mn 0.7-0.9%, La 0.006-0.008%, Ce 0.006-0.008%, with the remainder being Fe and unavoidable impurities; The preparation of the high-strength corrosion-resistant steel bar includes the following steps: S1: Raw material smelting and composition positioning: Molten iron and clean scrap steel are loaded into the converter according to the heat balance ratio. 90 seconds before the end of blowing, Cu, Cr, Ni and Mo alloy ladles are added sequentially. At the end of blowing, deoxidizer FeSi is added and the carbon content at the end is controlled. After tapping, Ar-N mixed gas is introduced into the ladle for stirring to uniformly dissolve Nb, V and Ti micro-alloy wires. When the total oxygen in the ladle reaches the standard, it is transferred to the next refining stage. S2: RH Vacuum and LF Ultra-Clean Refining: After completing step S1, the ladle is placed in the RH vacuum chamber, evacuated, and argon gas is introduced for treatment; after returning to normal pressure, it is transferred to the LF refining furnace; Ca / Al is fed into the Ca wire in proportion within the first 8 minutes to maintain the temperature of the molten steel. After the Ca treatment is completed, FeB cored wire is continued to be fed. After the oxygen potential reaches the target at the end of the refining, the next step of continuous casting is then carried out. S3: Rare earth wire feeding and light pressing in continuous casting zone: After completing step S2, the Ø11mm La-Ce cored wire feeder is started simultaneously during ladle casting, and rare earth is added slowly and uniformly below the surface of the molten steel in the crystallizer; the slag surface is covered with low-viscosity emulsified powder, and light pressing is carried out in the secondary cooling zone using the billet, and then cooled by mist cooling. S4: Thermomechanical Controlled Rolling: After completing step S3, the billet is hot-sent into a walking beam heating furnace and heated to a uniform temperature of 1050-1080℃. The temperature in the roughing zone decreases from 1050-1080℃ to 980℃, with a total reduction of 30%. The temperature in the finishing zone decreases from 980℃ to 880℃, with a reduction of 45%. The steel bars exiting the finishing zone are conveyed at a uniform speed via the discharge roller conveyor, and the average temperature of the steel bars is maintained at 870-880℃. S5: Online quenching: After completing step S4, the rolled steel bars are uniformly introduced into the water mist-air curtain combined quenching box for cooling. When the temperature is cooled to 260℃, it is held for 1 to 1.5 seconds, and then naturally convective cooling is performed. S6: Medium-temperature distribution and tempering: After completing step S5, the steel bars are removed from the quenching box and heated to 430-460℃ via a 14m slide rail, held at a constant temperature for 100-140s, and then air-cooled to room temperature. S7: Zn-Al-Mg micro-plating and rare earth post-treatment: After completing step S6, the steel bar is heated and then immersed in the Zn-Al-Mg liquid bath for plating; after taking it out of the bath, an air knife is used to quantitatively control the coating, and the steel bar is placed in room temperature humid air for deliquescence-drying cycle. S8: Finished product aging and inspection: The finished steel bars are subjected to low-temperature heat treatment to relax stress, natural aging treatment, and then non-destructive testing of the entire steel bar is carried out using electromagnetic eddy current and online ultrasonic equipment. Subsequently, the steel bars are cut and bundled according to length.

2. A high-strength corrosion-resistant steel bar according to claim 1, characterized in that, In step S1, the molten iron has P≤0.03% and S≤0.015%; the weight ratio of the molten iron to scrap steel is 68~72:28~32.

3. A high-strength corrosion-resistant steel bar according to claim 2, characterized in that, In step S1, the Ar-N mixed gas flow rate is: Ar 30L / min, N 20L / min.

4. A high-strength corrosion-resistant steel bar according to claim 3, characterized in that, In step S3, the specific parameters for the uniform and slow addition are: 1 to 1.5 m / min; the low-viscosity emulsifying powder is composed of CaO, SiO2, Al2O3, CaF2, Na2O, K2O and C in a mass ratio of 29 to 33:30 to 32:5:6:3:5:

4.

5. A high-strength corrosion-resistant steel bar according to claim 4, characterized in that, In step S5, the steel bar introduction speed parameter is 8-10 m / min; the parameters of the water mist-air curtain combined quenching box are: water pressure of water mist section 0.45-0.65 MPa, compressed air pressure of air curtain section 0.25-0.35 MPa, length of water mist section 1.2-1.5 m, and length of air curtain section 0.6-0.8 m.

6. A high-strength corrosion-resistant steel bar according to claim 5, characterized in that, In step S7, the Zn-Al-Mg liquid tank is composed of the following raw materials in percentage: Zn 96.6-97.6%, Al 1.2-1.7%, Mg 1.2-1.7%.

7. A high-strength corrosion-resistant steel bar according to claim 6, characterized in that, In step S7, the quantitative control parameter for the coating is 25-35 g / m³. 2 .

8. A high-strength corrosion-resistant steel bar according to claim 7, characterized in that, In step S7, the parameters of the ambient temperature and humidity air are: temperature 20-30℃, relative humidity 70-80%.

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